Cutting oil composition



, operations.

CUTTING OIL COMPOSITION Everett c. Hughes, Shaker Heights, and HarrisonM. Stine, Lyndhurst, Ohio, assignors to The Standard Oil Company,Cleveland, Ohio, a corporation of Ohio No Drawing. Application May 19,1954, Serial No. 430,972

2 Claims. (Cl. 252-45) The present invention relates to a cutting oilconcentrate, cutting oils containing such a concentrate andcharacterized by a unique combination of superior cutting ability andabsence of the formation of disagreeable odors when in use, and to amethod of making the concentrate.

Oils containing sulfur or sulfur compounds dissolved therein have beensuggested heretofore as cutting oils. Such oils also frequently containchlorine and a.fatsuch as lard oil. It is believed that the sulfur, tobe effective in improving the cutting ability of a cutting oil, must be11 an active form, i. e., not bound to a carbon atom, which can reactwith metal being machined under the condition existing at the point ofcontact between the tool and the machined metal. Heretofore, the amountof active sulfur which could be incorporated into an oil has beendependent largely upon the solubility of free sulfur in the oil and uponthe amount of sulfur which can be chemically combined but not bound to acarbon atom.

A great many suggestions have been made heretofore for increasing theactive sulfur content of cutting oils. In some instances, thesesuggestions have resulted in oils having excellent cutting ability butpoor odor characteristics and/or stability. In other instances, theyhave resulted in oils of acceptable odor but of poor cutting ability.Generally it has been found that some compromise must be made amongodor, stability, and cutting ability factors, the cutting ability beingimproved with an increase in sulfur content at the expense, however, ofodor and stability.

The odor characteristics of a cutting oil are not necessarily apparentupon an examination of the oil as produc'ed or supplied to a user. Inmany instances, odors are developed only when the oil is used inmachining This is apparently due to the formation of odoriferouscompounds under the conditions prevailing at the cutting tool. If thecutting oil develops an unpleasant or obnoxious odor during use, itmakes no difference how good the oil is from the standpoint of cuttingability, i. e., the number of pieces that can be machined with a giventool, the wear on the tool and the surface finish of the metal beingmachined because machinists will refuse to work with it.

Hydrocarbon polysulfides containing one or more alkyl unpleasant doorthat is characteristic of the polysulfide itself rather than of amercaptan impurity, since it cannot be altered by caustic washing, anddiallyl tetrasulfide nited States PatentO 2 I which, because of itslight yellow color, ready miscibility with mineral oil and very highsulfur content appeared very promising, was found to have a nauseatinggarlic odor. The few polysulfides in this group that do not possess suchodors initially, almost without exception develop odors, upon use, thatare or soon become so obnoxious as to cause machinists to walk off thejob. in some instances the odors developed during use do not seem toounpleasant at first but for some reason become intolerable uponcontinued use due to a subtle accumulation of odors in high speed,automatic, multispindie machines, because of the large volumes of oilthey require and the heat, violet agitation and splashing to which theoil is subjected.

lroposals to utilize aryl sulfides in cutting oils relate generally tothose aryl sulfides in which a sulfur atom or a chain of sulfur atoms issubstituted directly on the aromatic nucleus. Thus, for example,proposals have been made to utilize aryl sulfides, such as phenyl-,tolyl-, xylyl-, naphthyland anthracene sulfides in cutting oils withoutsuggesting that there are any material differences among the many arylsulfides that would make some of them less suitable than others.

It has also been proposed in the art to utilize in cutting oils arylsulfides in which the sulfur atoms or chains of sulfur atoms areconnected to the aromatic nuclei by methene or ethene groups. Theseproposals are limited, however,- to aryl sulfides in which one methylgroup and, in one unsupported, purely prophetic proposal, two methylgroups, are substituted on the aromatic nuclei and in which the numberof sulfur atoms is limited to two despite generalizations as topolysulfides. It appears to be generally believed in the art that inthis more limited class or aryl sulfides, the monosulfides anddisulfides are to be preferred over sulfides containing more than twosulfur atoms and the unsubstituted aryl sulfides are to be preferredover substituted aryl sulfides. This preference is apparently based onconclusions by some investigators that the lengthening of the sulfurchain and the substitution of alkyl groups on the aryl nuclei would bothcontribute to reducing the oilsolubility of such compounds and to makingthem solid rather than liquid at ordinary temperatures.

The surprising and unexpected discovery has now beenmade that it isfeasible to prepare alkyl-substituted benzyl polysulfides, a termintended herein to include the various isomeric forms oftrimethylbenzyl, methylethylbenzyl,

propylbenzyl and isopropylbenzyl polysulfides, as well as.

mixtures thereof, which contain ten carbon atoms in eachalkyl-substituted benzyl group and are characterized by appreciablyhigher total and active sulfur content and molecular weight than hashitherto been considered possible. These compounds have the empiricalformula CzoI-lzeS: and are characterized by the general formula R1SX-R2in which R1 and R2 are alkyl-substituted benzyl radicals each having atotal of ten carbon atoms and x is between about 4 and 5. R1 and R2 maybe the same or different so long as each is a trimethylbenzyl,methylethylbenzyl, propylbenzyl or isopropylbenzyl radical. Thecompounds are liquid at room temperature,

readily soluble in cutting oil bases, substantially odorless, and havelow volatility and excellent adherence to cutting surfaces at hightemperature, all properties that are highly desirable in cutting oilsand cutting oil concentrates.

ethyl-, proplyand isopropylbenzyl halides, with an excess ofalkali-metal polysulfide and elemental sulfur at an elevatedtemperature. The reactants may all be mixed together and reacted in asingle step. It is preferred, however, first to react one or more of thealkyl-substituted benzyl chlorides with. alkali-metal tetrasulfide toform alkyl-substituted benzyl polysulfides containing an average of atleast about three and preferably about four sulfur-atoms per molecule.These polysulfides are highly useful, as cutting oil concentrates butare then preferably reacted with elemental sulfur to formalkyl-substituted benzyl, polysulfides containing an average of betweenabout four and five, and preferably close to five, sulfur atoms permolecule.

'In accordance with one embodiment of the method of the invention,preferred because of the ready availability of the starting material, acatalytic reformate containing a mixture primarily of the variousisomers of trimethylbenzene and methylethylbenzene is chloromethylatedby .anysuitable means such as, for example, by reaction withformaldehyde, or a formaldehyde engendering material, and HCl in, theform of hydrochloric acid, hydrogen chloride gas, or both, for fromabout two to about seven hours at temperatures of the order of about l50F. This reaction is advantageously carried out while stirring thereactants under a reflux and, after thereaction is completed to theextent desired, cooling the reaction mixture-to room temperature,separating the two'immisciblephases, washing theupper oily layer withwater and separating the aqueous phase, washing the upper layer withsodium carbonate solution until the products are neutral, separating thelayers, washing the products aglain with water and separating thelayers, andfinally drying the'products with anhydrous calcium chloride.The organic reaction .product so obtained after removal of anyxylylenedichlorides formed, is a mixture, which may if desired be diluted withunreacted benzenes, of aromatic moriochlorides. These monochlorides areprimarily the isomers of trimethylbenzyl chlorides having the formula(CHshCsHzCHzCl. Methylethylbenzyl chlorides having the formulaCH3(C2H5)C6H3CH2C1, and propyland .isopropylb'enzyl chlorides having theformula (C3H7)CsH4CHaC1,may also be included.

, The mixture of aromatic monochlorides obtained in thisfr'nauner, orany oneor combination of alkyl-substituted beniyl halides containing tencarbon atoms from aiiyother source, is reacted at an elevatedtemperature of the order, of about 200 F., for several hours with anexcess 'of'sodiurnltetrasul fide in the form of an aqueous solution,preferably with agitation under an inert atmosphere such asnitrogen.Upon cooling and settling, the reaction mixture forms an upper organicphase and a lower aqueous phase. The lower aqueous phase is separatedand the remainder, i. e., the upper organic phase, is washed with analkali-metalhydroxide solution. Upon separation of the alkali-metalhydroxide solution, high yields of alkyl-substituted benzyl polysulfideshaving ten carbon atoms in each benzyl radical and containing an averageof at least about three and generally about four sulfur atoms permolecule are obtained. For convenitime, these are referred to herein asalkylbenzyl tetrasulfides. I

The reaction between the halides and alkalimetal tetrasulfide ispreferably carried out in the presence of a diluent having a lowviscosity and a highflash point. Hydrocarbon fractions having boilingpoints ranging from the kerosene to the fuel oil boiling ranges,generally designated as gas oil, are particularly suitable for thispurpose. 'I'he'addition of a gas oil orfuel oil, which doesnot reactwith 'either the reactants, the alkyl-sub stituted benzyl tetrasulfidesor the ultimately desired alkyl-substituted benzyl'pentasulfides, hasthehighly desirable and purely physical functions of imparting to themixtures thereof lower viscosities than either the tetrasulfides or thepentasulfides per se, facilitating the handling of the reactants and theproducts, and aiding in the separation of any aqueous phase after the.:reaction, :Alkylsubstituted benzenes, having boiling points *aboveabout 300 F.,=such as any 'thatfiniay be unreacted "in theFchloromethylation "described,:are "also *e'ruinently suitable asdiluents. The

diluent remains with the organic phase and serves as such isthesucceeding reaction step with elemental sulfur.

The alkylbenzyl tetrasulfides obtained by reaction between the benzylchlorides and sodium tetrasulfide are then reacted, preferably whileremaining in the presence of the diluent, with an excess, preferably 5%,of elemental sulfur for two to three hours at a temperature betweenabout 200 F. and about 300 F., preferably about 240 F., to form thecorresponding alkyl-substituted benzyl polysulfides having ten carbonatoms in each benzyl radical and containing an average of between aboutfour and five and preferably close to five sulfur atoms per molecule.For convenience, these are referred to herein as thealkylbenzylpentasulfides.

In another emb diment of the method of the invention, which involves ahigher consumption of sulfur, the alkylbenzyl pentasulfides are prepareddirectly by admixing alkylbenzyl chlorides simultaneously with an excessof sodium polysulfide and an excess of elemental sulfur and reacting ata temperature below the boiling point of the lowest boiling component inthe reaction mixture, e. g., between about 150 F. and about 250 F. Thetemperature and time of reaction preferred, to avoid settling out ofsulfur from thezproduct upon prolonged standing, are about 200 F. andabout 2 hours.

It:is tob'eunderstood, of course, that it is within the scope of theinvention toprepare any one or a selected combination of the possibleisomers of the trimethyl' benzyl, methylethylbenzyl, propylbenzyl andisopropylbenzyl'polysulfides by appropriate isolation of thecorrespondiug isomeror isomers of the starting material.

Both the alkylbenzyl tetraand pentasulfides, diluted or not =with"asuitable hydrocarbon diluent such as gas oil, may be blended toformstable and clear solutions with any mineral cutting oil base, e. g.,a hydrocarbon oil, such "as an acid-treated oil, "having a viscositybetween about 75 and 300 SSU at 100 F., and said cutting oil a basemayitself contain free sulfur dissolved therein. The

lower limit :of viscosity specified is imposed largely by sulfursolubility. (Dils having viscosities higher than 300 SSUat 100 'F.arenot preferred because of difficulties of handling and flowing. Cuttingoil blends containing as little-as 0.5% or less by weight of alkylbenzyltetrasulfide or pentasulfide have excellent cutting ability.Concentrates containing as much as about to 70% or more of alkylbenzyl'polysulfide in gas oil or other hydrocarbon diluent, without beingblended with a cutting oil base,

' have superior cutting ability and excellent odor characteristics. Theconcentrates of the invention, apparently because of their highermolecular weight and surprisingly high content of active sulfur, combinethis unusually excellcnticutting abilitylwith low volatility, ability tostay on the tooland the work at the cutting point, absence ofobjectionable'o'd'oreither upon standing or in severe use and ability toform stable blends with mineral cutting oil Ebases. For cuttingoperations on ductile steels, sulfurized oil blends containing betweenabout 0.5% and about 5% "by weight of the concentrate are highlysatisfactory.

Perhapsthe'most surprising characteristic of the alkylbenzyltetrasulfide and pentasulfide cutting oil concentrates of the inventionis that they make it possible to incorporate into a cutting oil blendmore active sulfur than isrequired'oridesired forsome types of cuttingoperations. .The present invention, therefore, provides anexcellent;rneans of controlling accurately the amount of active sulfurinarcutting oil so that it will be the optimum amount. foranypa'rticul'ar metal cutting operation. It is alsopossible to add smallamounts of other ingredients, e..g.', 1%. by volumelardoil, that maskthe effect of excess active sulfur. git is-to be-"und'ei stood thatwhilethe products of this 1nv'ention 'eoiisist essentially of one oracombination of alhyl sub" polysulfides containing ten carbon atomsdneach benzyl groupy'preferably diluted with unsulfurized gas oil orblended with a mineral cutting oil base or both, conventional additivessuch as lard oil, graphite and oil-soluble chlorinated compounds such aschlorinated wax and chlorinated aromatics typical of which ischlorinated biphenyl and the like may be added inamounts that do notmaterially alter the character of the products. It is also within thescope of the invention to add minor proportions, i. e., of the order of1% or less, of antioxidants.

The blending of the cutting oil of the invention with lard oil in anappreciable amount, i. e., above about 1%, and preferably from about 2to 10% by volume, is particularly desirable and advantageous forreducing tool wear when cutting operations are carried out on abrasivesteels and has the further advantage of providing a cutting oil that ismost universally useful on both abrasive steels and ductile steels.ferred cutting oil is a blend of a mineral cutting oil base with about4% by volume lard oil and about 1% by weight of a 60/40 mixture ofalkylbenzyl polysulfide and gas oil. It is to be understood, therefore,that it is within the scope of the invention to add amounts of lard oilwhich do alter somewhat the character of the alkylbenzylpolysulfide-containing cutting oils of the invention in so far as themachining of abrasive steels is concerned.

The advantages and utility of the cutting oil concentrate, cutting oiland method of this invention will become more apparent from thefollowing example illustrating the invention.

EXAMPLE Part A 120 parts by weight of Solvesso 100, a catalyticreformate comprising a mixture of 4% aliphatic hydrocarbons and 96%aromatic hydrocarbons containing approximately 39% by weighttrimethylbenzene isomers (7% 1,3,5-trimethylbenzene, 27%1,2,4-trimethylbenzene and 1,2,3-trimethylbenzene), 36% by weightmethylethylbenzene isomers (20% l-methyl-3-ethylbenzene, 8%1-methyl-4-ethylbenzene and 8% 1-methyl-2-ethylbenzene), 3%isopropylbenzene and minor amounts of m-xylene (3%), o-xylene (6%),p-xylene (trace) and (13%) unidentified monoalkylbenzenes probablyincluding n-propylbenzene isomers, were refluxed at 140 to 158 F. forseven hours under a water condenser while stirring the reactants with525 parts by weight of 36% aqueous hydrochloric acid and 42.8 parts byweight of 91% paraformaldehyde in the form of flakes. During thereaction a slow stream of HCl gas was fed to the reaction mixture andcare was taken to provide good ventilation. After seven hours, thereaction mixture was cooled to room temperature and allowed to settleinto two immiscible layers, the lower aqueous layer was separated, theupper oily layer was washed with water, then washed with a 5% aqueoussodium carbonate solution until neutral and then washed again andfinally dried with anhydrous calcium chloride.

55% of the final oily phase was found to be a mixture ofalkyl-substituted benzyl chlorides having the empirical formulaC1oH13Cl, 19% was found to be a mixture of alkyl-substituted xylylenedichlorides and the remaining 26% was found to be substantiallyunreacted. The products were then subjected to vacuum distillation toseparate the alkylbenzyl chlorides and unreacted alkylbenzenes from thealkylxylylene dichlorides.

Part B 168.5 parts by weight of the alkylbenzyl chlorides of Part A wereadmixed with 368 parts by weight of a 40% aqueous solution of sodiumtetrasulfide (approximately a 30% excess of the tetrasulfide to insurecomplete reaction of the chloride) and with 132 parts by weight of a gasoil having a viscosity of 42 SSU at 100 F. and a flash point at 275 F.The mixture was heated to 200 F. and maintained at that temperature forfrom 3 to 5 One example of such a pre- I hours while stirring well. Thereaction products were then cooled and allowed to settle, the loweraqueous phase was separated and the remaining organic phase washydroxide solution per 5 parts by volume of organic v phase, and themixture was stirred for thirty minutes, the

caustic then being separated. Thereupon, 3% Super Filtrol, a mineraladsorbent, was added and the mixture stirred for about ten minutes. Themixture was then filtered to yield 94 to 99% of the theoretical yield ofalkylbenzyl polysulfides in the gas oil.

The product was a 60/40 mixture of alkyl-substituted benzyltetrasulfides, having the empirical formula CZOHZSSx, and gas oil havinga total sulfur content of 18.5% (95% of the theoretical 19.4% totalsulfur content, or containing an average of about four sulfur atoms permolecule of polysulfide) and an active sulfurcontent of 8.7% (90% of the9.7% theoretical active sulfur content). 1

Part C 329 parts by weight of the 60/40 mixture of alkylbenzyltetrasulfide and gas oil prepared in accordance with part B of theexample were admixed with 16 parts by weight of elemental sulfur andsufficient additional gas oil, about 10 parts by weight, to maintain theratio of polysulfide to gas oil at about 60/40. The mixture was then.stirred for 2 hours under nitrogen atmosphere at a temperature of 240 F.

The total sulfur content of the alkyl-substituted benzyl pentasulfides,likewise having the empirical formula C20H26Sx, analyzed 22.9% (98% ofthe theoretical 23.5%, or containing an average of about five sulfuratoms per molecule) and the active sulfur content analyzed 15.1% (105%of the theoretical active sulfur con tent of 14.3%). The amount ofsulfur introduced was about equal to the theoretical amount consideringthe precision of the available analytical methods.

Part D A cutting oil base was prepared by adding, to Diamond Paraiiinoil, an acid treated lubricating oil stock having a viscosity of SSU at100 F., 0.8% by weight elemental sulfur, i. e., the maximum amount ofsulfur soluble in the oil at 0 C. The mixture was heated and stirred at240 F. until all of the sulfur was dissolved. This took approximatelyone to two hours.

Blends of the cutting oil base with 0.5 to 5% by weight of the 60/40alkylbenzyl tetrasulfides-gas oil concentrate prepared in Part B of theexample and with 0.5 to 5% by weight of the 60/40 alkylbenzylpentasulfides-gas oil concentrate prepared in Part C of the example formexcellent cutting oils characterized by remarkable cutting ability, lowvolatility and absence of odor, and ability to remain on the work andthe tool at the point of cut. A blend of cutting oil base with 1% byvolume of the 60/40 alkylbenzyl pentasulfide-gas oil concentrate, 4%lard oil and 0.5% Aroclor 1254, a chlorinated biphenyl available as ayellow-tinted, viscous oil having a chlorine content of 54%, a specificgravity between 1.538 and 1.548 and a distillation range of 365-390"(3., was found to be particularly effective.

it is obvious that in the foregoing example bromine or iodine can besubstituted for chlorine and that likewise potassium tetrasulfide can beused in place of sodium tetrasulfide. Chlorine, alkyl-substituted benzylchlorides, and sodium tetrasulfide are preferred because they arerelatively inexpensive and most readily available.

It is to be understood that these and other modifications of the methodand products described herein will readily occur to those skilled in theart. All such modifications are intended to be included within the scopeof the invention as defined in the accompanying claims.

We claim:

1. A cutting oil concentrate comprising from about 50 to about 70% byweight of a mixture of organic polytreated with one part by volume of a3% aqueous sodium 1 5 18 t e mul wherein R1 and R2 are selected from thegroup consisting of three methyl radicals, one methyl and one ethylradical, and one propyl radical, and x averages between about 4 and 5,said mixture having been derived from a mixture of aromatic hydrocarbonscontaining approximately 9% xylenes, 3% isopropyl benzene, 36% methylethylbenzenes 39% trimethylbenzenes, and 13% mixed monoalkylbenzenes, bychloromethylation and reaction with sodium tetrasulfide, and with sulfurwhen x is in excess of 4,,and from about 50 to about 30% by weight of ahydrocarbon diluent.

2. A cutting oil comprising a mineral oil and from about 0.5 to about byweight of a mixture of organic polysulfi des having the formula where R1and R2 are selected from the group consisting of three methyl radicals,one methyl and One ethyl radical, and one propyl radical, and x averagesbetween about 4 and 5, said mixture having been derived from a mixtureof aromatic hydrocarbons containing approximately 9% xylenes, 3%isopropyl benzene, 36% methyl ethylbenzenes, 39% tn'methylbenzenes, and13% mixed monoalkylbenzenes, by chloromethylation and reaction withsodium tetrasulfide, and with sulfur when x is in excess of 4.

References Cited in the file, of this patent UNITED STATES PATENTS2,113,092 Moran et a1 Apr. 5, 1.938 2,185,008 Wojcik Dec, 26, I9392,273,471 Kimball Feb. 17, 1942 2,538,941 McCallum Ian. 23, 676,987Lewis et a]. Apr. 27, 1954

2. A CUTTING OIL COMPRISING A MINERAL OIL AND FROM ABOUT 0.5 TO ABOUT 5%BY WEIGHT OF A MIXTURE OF ORGANIC POLYSULFIDES HAVING THE FORMULA